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Biomedical subjects

B Lahlou

Publications and source records attributed to B Lahlou.

At least 37 records · Page 2Linked to original sources
PubMed1987

Adenylate cyclase activity in fish gills in relation to salt adaptation.

The influence of salt adaptation on specific adenylate cyclase activity (measured by conversion of [alpha-32p]-ATP into [alpha-32p]-cAMP) was investigated in gill plasma membranes of rainbow trout (Salmo gairdneri) adapted to various salinities (deionized water, DW; fresh water, FW; 3/4 sea water, 3/4 SW; sea water, SW) and in sea water adapted-mullet (Mugil sp.). Basal activity declined by a factor of 2 in trout with increasing external salinity (pmoles cAMP/mg protein/10 min: 530 in DW, 440 in FW, 340 in 3/4 SW; 250 in SW) and was very low in SW adapted-mullet: 35. The Km for ATP was similar (0.5 mM) in both FW adapted- and SW adapted- trout in either the absence (basal activity) or in the presence of stimulating agents (isoproterenol; NaF) while the Vm varied. Analysis of stimulation ratios with respect to basal levels of the enzyme showed that hormones (glucagon, VIP) and pharmacological substances (isoproterenol, NaF) display a greater potency in high salt than in low salt adapted- fish gills. In contrast, salt adaptation did not have any effect on the regulation of adenylate cyclase by PGE1. These results are interpreted in relation to the general process of osmoregulation.

Adaptation, Physiological↗
PubMed1987

Basal and stimulated adenylate cyclase activity in the gill epithelium of the rainbow trout.

Basal and stimulated adenylate cyclase specific activity was characterized in gill plasma membrane of freshwater-adapted trout by measuring the conversion of [alpha-32P]ATP into [alpha-32P]cyclic AMP. Both basal and isoproterenol- or sodium fluoride-stimulated enzyme activities were linear with time and protein concentration. The optimum activities were obtained using a pH buffer of 7.5 and a temperature of 20 degrees. The Km for ATP was 0.5 mM in the presence or absence of the stimulators. The presence of 10(-5) M guanosine-5'-triphosphate and 4 X 10(-3) M MgCl2 (2.41 X 10(-3) M free Mg2+) was required to optimize not only the basal activity but also the stimulation ratio (test/control) produced by these agents. On the contrary, Ca2+ was inhibitory. IC50 for CaCl2 was 5 X 10(-4) M (10(-7) M free Ca2+) in the presence or absence of the stimulators. Under these conditions, the basal adenylate cyclase specific activity was 400-450 pmol/mg protein/10 min. A maximal stimulation was produced by isoproterenol or PGE1 10(-5) M (50% increase over basal activity) or by glucagon 5.7 X 10(-10) M (30%). In addition, this enzyme displayed high sensitivity to sodium fluoride which induced a particularly large maximal effect (370%) at a concentration of 10(-2) M.

Adenosine Triphosphate↗
PubMed1987

The cellular mechanism of the antiandrogenic action of nomegestrol acetate, a new 19-nor progestagen, on the rat prostate.

Nomegestrol acetate, like other synthetic progestins such as medroxyprogesterone acetate (MPA), chlormadinone acetate, megestrol acetate and cyproterone acetate, is able to modify the physiological actions of androgens. In the present study, the effects of nomegestrol acetate and other antiandrogens on the binding of androgen to the androgen receptor (AR) and on the 'activation' of this receptor were investigated, using rat ventral prostate as target model. Relative binding affinities (RBA) for AR were first estimated in vitro with respect to [3H]testosterone for a series of structurally-related compounds. The values obtained ranged as follows: dihydrotestosterone (DHT) much greater than megestrol acetate greater than or equal to testosterone (T) greater than nomegestrol acetate greater than 19-nor progesterone (19NP) greater than progesterone (P). An assay was established, using two different incubation times (3 h and 24 h) to further investigate relationships between binding affinity and androgenic, or antiandrogenic, activity. The following order (as %) was obtained for progestins as against [3H]mibolerone (DMNT): 1) DMNT (100) much greater than nomegestrol acetate (42) greater than megestrol acetate (29) greater than chlormadinone acetate (9) greater than MPA (8) greater than cyproterone acetate (6) after 3 h and 2) DMNT (100) much greater than MPA (53) much greater than nomegestrol acetate (19) greater than megestrol acetate (12) greater than chlormadinone acetate (14) and cyproterone acetate (8) after 24 h. Since the RBA of nomegestrol acetate declined with time, these results indicate that this substance may act like an antiandrogen rather than an androgen, while the contrary prevails concerning MPA.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgen Antagonists↗
PubMed1986

In vitro studies on the release of cortisol from interrenal tissue in trout (Salmo gairdneri)--II. Action of changes in extracellular electrolytes.

Secretion of cortisol by the interrenal tissue of the trout Salmo gairdneri was studied in vitro by a perifusion method in relation to the effects of electrolyte concentrations in the medium. An increase in osmotic pressure (produced by adding mannitol or NaCl) induced an immediate, but brief augmentation in cortisol release. Suppression of Na+ had no effect while its reintroduction in the medium led to stimulation of hormone release. By contrast, a sharp peak was obtained whenever Cl- concentration was dropped (by 50 mM fractions). These opposite effects of Na+ and Cl- when they vary independently of each other is interpreted with regard to osmoregulation and acid-base regulation. Raising K+ even to high levels (up to 20 mM) produced no change. The absence of Ca2+ had no obvious effect while its addition induced an immediate peak of cortisol release. In addition, external Ca2+ proved necessary for the action of ACTH to occur. These results establish that cortisol release in trout may be directly affected by changes in electrolyte concentrations in the extracellular space.

Adrenal Glands↗
PubMed1986

Ion-selective micro-electrode studies of the electrochemical potentials in trout urinary bladder.

Intracellular micro-electrode techniques were used to measure the electrical resistances of the cell membranes and the shunt pathway and intracellular ionic activities in trout urinary bladder when the tissue was incubated in Ringer solution and in the presence of the polyene antibiotic ionophore amphotericin B. In control conditions the transepithelial potential was zero and the intracellular potential was -56 mV. The intracellular ionic activities measured with single- and double-barrel ion-sensitive micro-electrodes for the first time in a fish bladder (aiNa = 16 mM, aiK = 87 mM, and aiCl = 21 mM) indicate an active accumulation of K and Cl ions and an active extrusion of Na ions by the cell. The maintenance of intracellular Cl activity above its equilibrium value depended on the presence of Na ions in the mucosal medium, but was independent of the presence of K ions. Flat cable analysis yielded values for transepithelial, apical, basolateral and shunt resistances of 197, 2790, 1986 and 205 omega cm-2 respectively. Equivalent circuit analysis using amphotericin B yielded similar values for shunt resistance. The paracellular pathway accounts for 96% of transepithelial current flow and this epithelium may be classified as 'leaky'. The cells are electrically coupled with a space constant of 354 micron. Amphotericin B when added to the mucosal solution induced an immediate serosa positive transepithelial potential of about 9 mV and a short-circuit current of 64 microA cm-2. The Vt was ouabain sensitive and dependent on mucosal Na concentration. The origin of the antibiotic induced transepithelial potential was an increase in the sum of the cell membrane electromotive forces. The apical membrane potential depolarized to -7 mV and its resistance fell to 433 omega cm-2. During the first 10 min of exposure aiNa increased to 80 mM and aiK decreased to 7 mM with only a small change in aiCl. The changes in cellular Na+ and K+ activities were in accordance with their passive redistribution down their electrochemical gradients.

Amphotericin B↗
PubMed1986

Steroid regulation of Na+/K+-ATPase activity in the rat kidney: effect of a new 19-nor-progestagen.

The effects of Nomegestrol acetate (17 alpha-acetoxy-6-methyl-19-nor-4,6-pregnadiene-3,20-dione), a new 19-nor-progesterone derivative, on renal Na+/K+-ATPase activity were assessed in normal and adrenalectomized rats, and compared with the stimulatory or inhibitory actions produced by other steroids. This compound displayed an inhibitory effect which was similar to, but smaller than, that induced by progesterone and quite distinct from the stimulation produced by 19-nor-progesterone and corticosteroids. In addition, unlike progesterone, it did not antagonize the effect of aldosterone in adrenalectomized rats. This result, together with previous in-vivo and in-vitro observations on this compound indicates that additional modifications introduced in the molecular structure of 19-nor-progesterone produces a potent progestagenic substance virtually devoid of effects on renal Na+/K+-ATPase activity and sodium loss in urine.

Adrenalectomy↗
PubMed1985

In vivo and in vitro studies on the release of cortisol from interrenal tissue in trout. I. Effects of ACTH and prostaglandins.

The secretion of cortisol from the interrenal tissue in trout Salmo gairdnerii was studied in vivo and by an in vitro superfusion method in relation to the effect of adrenocorticotropic hormone (ACTH), prostaglandins (PGE1, PGF2 alpha) and prostaglandin inhibitors. The experiments were performed between April and July. In control, uninjected animals, circulating cortisol was 206 +/- 24 ng/ml. At 24 h following the intraperitoneal injection of indomethacin, dexamethasone, or both, the levels were reduced to 84 +/- 10, 43 +/- 20 and 63 +/- 11 ng/ml respectively. In control animals receiving solvent (ethanol), the value was 190 +/- 30. With longer term duration (72 h) the levels of plasma cortisol following injection of indomethacin, dexamethasone and both drugs together were 120 +/- 29, 120 +/- 10 and 37 +/- 8 respectively. On the contrary, no significant change was produced by prostaglandins. In vitro release of cortisol from superfused head kidneys (which contain the interrenal tissue of teleosts) decreased gradually with time and reached a minimum after 50 min. Addition of ACTH or of PGE1 to the medium induced an immediate, dose dependent increase in cortisol output which reached a maximum after 15-30 min. On the contrary, PGE2 alpha or indomethacin did not modify cortisol release. These results show that cortisol production in trout, which is controlled by ACTH as in other vertebrates, is also under the influence of other hormonal substances acting on the adenyl-cyclase system.

Adrenocorticotropic Hormone↗
PubMed1984

Nuclear binding of cortisol in intestinal mucosa and liver of a teleost fish (Salmo gairdnerii irideus).

Nuclear binding of corticosteroids in fish tissues was investigated in two target organs of the trout Salmo gairdnerii irideus: the liver and the intestinal mucosa. Incubation of intact nuclei with [3H]-cortisol or [3H]-dexamethasone failed to demonstrate high-affinity binding of these steroids to proteins. Exchange assay of [3H]-cortisol in high-salt nuclear extracts indicated an association constant Ka = 1.9 X 10(4) M-1 for intestinal mucosa and 2.1 X 10(4) M-1 for liver. In sea water-adapted trout, the association constant remained the same as in fresh water. These results extend previous observations obtained on the cytosol which showed that no high-affinity receptors could be disclosed in fish tissues using these two corticosteroids.

Animals↗
PubMed1982

Ion flux changes induced by voltage clamping or by amphotericin B in the isolated urinary bladder of the trout.

1. When bathed with Ringer solutions on both sides in Ussing chambers, isolated urinary bladders of trout carry out an electrically silent transport of Na+ and Cl- ions from mucosa to serosa. In the present experiments, an electrical gradient was set up across the epithelium mounted under these conditions either by using a voltage-clamp technique or by submitting the mucosal side to the polyene antibiotic Amphotericin B. 2. With stable potential differences between -40 and +40 mV applied to the tissue, both unidirectional fluxes (Jms and Jsm) for Na+ and for Cl- varied as a function of the electrical gradient. This indicates that a sizeable fraction of these ionic exchanges is due to passive diffusion across a low-resistance pathway. 3. Amphotericin B (40 micrograms/ml.) applied to the mucosal side induced an immediate and large (up to 50 mV, serosa positive) potential difference and a sustained diminution in tissue resistance. These effects were strictly Na+-dependent and were reduced in the presence of ouabain. Therefore they are due to increased passive entry of Na+ along its electrochemical gradient across the cellular apical membrane. 4. The effect of Amphotericin B was enhanced when Cl- was replaced by an impermeant anion such as gluconate. Therefore the shunting effect of Cl- on the induced potential observed in the control conditions appears to be due to an increase in Cl- permeability across an anion pathway. Flux data indicate that this pathway is transcellular.

Amphotericin B↗
PubMed1979

The mechanism of coupled transport of sodium and chloride in isolated urinary bladder of the trout.

1. Transepithelial fluxes of Na and Cl were measured in dissected trout bladders mounted in Ussing chambers. The mucosa-to-serosa fluxes appeared to comprise a linear and a saturating (Km = 8 mM) component as a function of the luminal concentration of the ion. The over-all permeability for Cl was higher than for Na. Removal of either ion from the mucosal side induced the disappearance of the net flux of the co-ion even when the substituting ions were not impermeant. This indicated a complete and specific mutual dependence between the Na and Cl transports. A large part (30-50%) of Cl exchanges was ascribed to an exchange-diffusion process. 2. In order to localize the site of ion copuling, the apical uptakes of Na and Cl were measured by short-term exposure (2 min) to radioisotopes. The apical fluxes were similar to the transepithelial fluxes and therefore appeared to be the limiting factor for ion transfer. Ionic replacements on the mucosal side showed that the coupling between Na and Cl and Cl/Cl exchange occurs at this step.

Animals↗
PubMed1978

[Cyclic AMP and control of ion exchanges in the fish intestine].

In isolated intestine of the European Flounder, cyclic AMP and theophylline induce a reduction of the negative transmural potential difference and short circuit current, increase severalfold the passive permeability for chloride and abolish the active transport of this ion. These effects are very different from those described in mammals.

Animals↗
PubMed1978

Uptake and binding of glucocorticoids in fish tissues.

Cytosols prepared from the liver and various tissues of goldfish (intact or hypophysectomized) and trout (intact) were incubated at 2 degrees C in the presence of tritiated cortisol or dexamethasone (3 x 10(-9) to 3 x 10(-6) mol/l) with or without a 1000-fold excess of unlabelled steroid. In contrast to mammals, the specifically bound component represented a very low fraction of the total bound steroid retained on DEAE cellulose filters and did not show saturation over a large range of concentrations. The subcellular distribution of [3H]dexamethasone was studied in trout liver after intra-vascular injection of the labelled steroid with and without an excess of unlabelled steroid. The amount of protein-bound steroid in the cytosol again corresponded to a small (4%) proportion of the free steroid. The large reduction in the uptake of tritiated dexamethasone, which was induced in both the cytosol and nuclei by competing unlabelled dexamethasone, was interpreted as evidence for mediated entry across cellular and nuclear membranes. These results indicate that high-affinity binding sites are absent, or present only in very small numbers in cytosol from teleost tissues. The entry of glucocorticoids into the nucleus may not require the hormone to be bound to high-affinity cytosolic receptors unless the binding, though quantitatively small, displays a high rate of turnover.

Animals↗
PubMed1975

Sodium and chloride transport by the intestine of the European flounder Platichthys flesus adapted to fresh or sea water.

1. Everted intestinal sacs prepared from Platichthys flesus adapted to sea water (SW) have higher rates of salt and water transport than did sacs prepared from fresh water adapted (FW) fish. 2. Intestines mounted in Ussing chambers gave stable open-circuit voltages and short-circuit currents after pre-incubation for 20--30 min of --1.91 +/- 0.14 (14) mV and --45.0 +/- 5.1 (14) muA/cm2, SW fish, and --1.24 +/- 0.14 (11) mV and --18.2 +/- 3.6 (11) muA/cm2, FW fish. 3. Isotope flux measurements indicated a net Na transport of 21.5 +/- 4.1 (11) neq/cm2-min in SW fish intestines, but no significant Na transport in FW fish (7.6 +/- 7.6 (9) new/cm2-min). Both preparations showed an active Cl transport, 26.6 +/- 6.1 (12) neq/cm2-min for SW and 18.5 +/- 9.7 (17) neq/cm2-min for FW fish. 4. No significant difference in the uptake of Na or Cl across the mucosa was observed between FW and SW fish. The uptake of both ions showed some saturation at high concentrations. 5. Interactions between Na and Cl uptake were small, although Cl uptake was significantly higher in Na-free solutions. 6. It is concluded that electrogenic Cl transport may be the dominant mechanism for water and salt transport in flounder intestine, and that adaptation to a saline environment involves regulation of pumping rather than Na or Cl entry across the mucosal membrane.

Animals↗
PubMed1975

[Adaptation of trout to seawater. Effects on sodium plasma concentration, gill exchange and intestinal transport].

10. Trout Salmo irideus are adapted to sea water (S W) within four weeks by submitting them to a stepwise increase in external salinity (successively: 1/3 SW, 1/2 SW, 3/4 SW, full SW). 20. In completely adapted individuals mean plasma electrolyte concentrations vary only slightly (by a few %) from one medium to another. Thus, the trout may be regarded as a euryhaline, eventually homeosmotic species. 30. With increasing outside salinity there is a progressive diminution in the overall gill permeability to ions which is suggested by saturation curves obtained for sodium fluxes (maximum at about 500 muEq/h. 100 g at 15 degrees C, for unshocked fish). 40. Disturbance of the animals provokes a striking elevation and desequilibrium in these exchanges and this in turn induces an abnormal rise in plasma concentrations and a subsequent failure to adapt to hypertonic media. 50. In vitro absorption of water and sodium by intestinal everted-sacs increases only after transfer to full sea water. Mucosal entry of ions into intestinal epithelial cells measured by the technique of Schultz et al. (1967), is diminished in sea water-adapted animal (by 42% in the case of sodium). 60. These results demonstrate that Salmo irideus possesses efficient osmoregulatory mechanisms which operate with minimal energy expenditure in hypertonic media.

Adaptation, Physiological↗